1. Field of the Invention
The present invention relates to computer bus interfaces, particularly to high-performance, high-bandwidth computer bus interfaces, and more particularly to a computer bus interface adapter with a predictive time base generator therein.
2. Background of the Invention
Computer processors typically communicate with cooperating components along one or more computer buses. Peripheral components, including audio, and print devices, portable storage media, and low-bandwidth networking devices usually are coupled with the bus through a peripheral or expansion computer bus interface adapter. On the other hand, devices with high bandwidth needs, including video, memory, high-performance networking, and core storage media often are linked to the CPU via a high-bandwidth local bus interface adapter. Components on expansion buses typically have operational speeds many orders of magnitude slower than that of the CPU; however, such components sporadically access CPU and system resources and, thus, critical design issues such as bus latency, setup and hold times, and clock-to-data time are of little import to interface adapters designed for those applications.
Although high-bandwidth, high-performance, local bus components and adapters tend to operate at clock speeds much higher than their expansion bus counterparts, they still lag current CPU speeds by about an order of magnitude. However, because local bus components tend to interact with the CPU to a significant degree, slow, inefficient, and poorly-designed local bus interface adapters can potentially waste substantial amounts of processor and system resources. Therefore, local bus interface adapters are usually faced with observing strict timing budgets when accessing and providing data to the local bus.
Many factors can lead an adapter to violate the timing budget imposed by a bus protocol. For example, delays introduced in the clock trees and in the data paths of bus adapters, or both, can effectively decouple the interface adapter from the bus, because the adapter response time fails to remain synchronized to the bus clock. The functional characteristics of VLSI devices employed in such high-bandwidth, high-performance computer bus interface adapters can be susceptible to design and process variations during manufacturing. Also, the response of such adapters can be compromised by variations in environmental conditions while operating.
There is a need, then, for a local bus interface adapter that mitigates critical path delays within a computer bus interface adapter, or device, to the extent that they do not violate the aforementioned timing budgets. It is desirable that such an adapter is robust to design and process variations during manufacturing, as well as to the environmental conditions, which may be encountered during operations. Because multiple local bus protocols exist in common computer environments, there also is a need for a robust, multiprotocol computer bus interface adapter that is observant of stringent bus protocol timing budgets.
The present invention satisfies the above needs by providing a predictive time base generator having predictive synchronizer and a replica delay element coupled with a feedback delay loop of the synchronizer. The predictive time base generator receives a clock signal delayed by a predetermined clock delay and produces a predictive time signal advanced in time by an amount represented by the replica delay element. Because it is desired that the replica delay element replicate one or both of the predetermined clock delay and the predetermined data delay, the predictive time base generator can substantially nullify the respective predetermined clock delay and the predetermined data delay. The replica delay element can include replicas of structure(s) found in an incoming clock path and an outgoing data path, such elements including, for example, voltage level shifters, buffers or data latches, multiplexers, wire element models, and the like, such that the time delay through the replica delay element can be adapted to match an undesirable time delay in a critical signal path of the device. The present invention also satisfies the above needs by providing a predictive computer bus interface adapter, which incorporates the aforementioned predictive time base generator. Such a predictive interface adapter can be adapted to be observant of stringent bus protocol timing budgets imposed under the PCI-X local bus protocol, and to be robust relative to variations in design and fabrication processes, and environmental operating conditions. In one embodiment of the present invention, the predictive interface adapter can be realized in a single-chip VLSI implementation, for example, an 0.18 micron CMOS VLSI implementation. Furthermore, it is preferred that the predictive interface adapter be a multiprotocol predictive interface adapter that can accommodate multiple computer bus protocols, including the PCI local bus protocol and the PCI-X local bus protocol, as well as similar bus protocols such as, for example, the CardBus protocol.